Corneal Degenerations and Infiltrations in Dogs
Corneal degenerations and infiltrations in dogs refer to abnormalities affecting the transparent lining covering the front exterior of the eyeball, including the iris and the pupil. This lining, known as the cornea, seamlessly transitions into the white part of the eye, called the sclera, which envelops the remainder of the eyeball. Positioned beneath the cornea and the sclera lies the stroma, a layer of connective tissue supporting the eyeball internally.
Corneal degeneration manifests as a unilateral or bilateral condition, often stemming from other ocular or systemic disorders. It is characterized by the accumulation of lipid or calcium deposits within the corneal stroma and/or epithelium, which is a layer of cells lining the inner cavity of the eyeball beneath the stroma. This medical concern can affect both dogs and cats.
Symptoms and Types
Symptoms and types of corneal degenerations in dogs often include a rough appearance of the cornea, marked by distinct margins where it meets the sclera. Conditions like corneal scars, corneal inflammation, or chronic uveitis (persistent inflammation of the front of the eye) can contribute to corneal degeneration. It is advisable to have the cornea examined for additional damage if any of these conditions are present, as early detection can help prevent severe and permanent damage.
Causes
The primary cause of corneal degeneration involves the accumulation of lipid (fat) deposits within the supportive structures of the inner eyeball, namely the stroma and the epithelium. Although lipids are essential components of living cells, excessive deposits in tissues can lead to disorders within the affected system. Systemic hyperlipoproteinemia, a metabolic disorder characterized by elevated levels of cholesterol and specific lipoprotein particles in the blood plasma, can heighten the risk of lipid deposits in the stroma or exacerbate existing ones. This condition can stem from secondary factors such as hypothyroidism, diabetes mellitus, hyperadrenocorticism (excessive cortisone production), pancreatitis, nephrotic syndrome (kidney damage), and liver disease.
Hypercalcemia, an excess of calcium production, can also increase the likelihood of calcium deposits in the stroma, contributing to corneal degeneration, although such deposits are less common than lipid deposits.
Other disorders impacting the cornea and its function include hypophosphatemia, an electrolyte imbalance characterized by insufficient phosphorus in the bloodstream, and hypervitaminosis D, the excessive production of vitamin D. Corneal degeneration is not inherited but exhibits a higher incidence rate among miniature schnauzers.
Diagnosis
During the diagnostic process, your veterinarian will observe several signs to arrive at a diagnosis. Your dog’s eyes will be treated with fluorescein stain, an orange dye viewed under blue light to identify corneal damage or the presence of foreign objects on the eye’s surface. This examination may reveal a corneal ulcer accompanied by varying degrees of swelling, visible as bluish to gray areas with indistinct margins, depending on the severity. Additionally, the stain can detect the presence of a corneal scar, which may cause opacity ranging from gray to white, depending on its severity. Advanced corneal ulceration may exacerbate the condition, potentially affecting vision. Severe vision impairment can result from underlying primary eye diseases like uveitis.
If no abnormalities are detected with the fluorescein stain, the veterinarian will examine for corneal stromal weakness (dystrophy), which affects both eyes and often leads to proportional focus issues. Affected corneas will appear gray to white with distinct margins and lack fluorescence staining, indicating the absence of eye inflammation. In cases where foreign objects have entered the eye (inflammatory cell infiltrate), the cornea may appear gray to white with indistinct margins. Microscopic examination of corneal cells may reveal the presence of white blood cells, responsible for defending the body against foreign materials and infection, indicating the presence of organisms in the eye.
Treatment
If an eye disease is diagnosed, your veterinarian will administer appropriate treatment. Lipid and calcium deposits that impair vision or cause discomfort to the eye, whether due to a roughened surface or disruption and ulceration of the corneal epithelium, may benefit from aggressive corneal scraping or superficial removal of part of the cornea (keratectomy). Following these procedures, medical management will be implemented as deposits are likely to reoccur in patients undergoing superficial keratectomy surgery. Your dog’s diet will also be taken into consideration. In cases of diagnosed hyperlipoproteinemia, a low-fat diet would be recommended to hinder further progression. Your veterinarian will provide guidance on dietary adjustments. Both treatment approaches can effectively slow or halt the progression of the disease.
Living and Management
Your veterinarian will aim to regularly monitor your dog’s serum cholesterol and triglyceride levels to evaluate the effectiveness of dietary management, if it has been advised as part of the maintenance plan. If a primary disease is detected, its progression or regression will be monitored, and treatment will be administered based on your dog’s comfort needs and medical indications.
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